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The three families of elementary particles and the arrow of time

Perhaps most intriguing fact in the world of elementary particles is the existence of three and only three families. The first is made up of quarks up and down with the electron and electron-neutrino. The same structure is repeated with the charm quarks and strange in the company of the muon and muon neutrino. The third replica lies with the family made up of top quarks and bottom, with the tauon and tau neutrino. Why

nature offers three replicates the same structure? This is a question of great depth and it questions the ultimate structure of the Standard Model of electroweak interactions. However, there is an observation that can not leave us indifferent. In the Standard Model is only possible to have violation of T (time reversal) if three or more families.

The T symmetry violation is an event truly exceptional. Implies that there are physical processes that can discriminate between it moves in one direction or the opposite. This violation of T, due to the presence of three families of elementary particles, is the only situation in which the laws governing the universe at the microscopic level selected arrow of time.

arrow Do not confuse this time with the second law of thermodynamics, which states what is the most likely development of a system of many particles. The thermodynamic irreversibility does not require a microscopic T violation.

The universe, therefore, opted to contain three and only three families of elementary particles and thus offer the option to distinguish between it moves in one direction or its opposite.

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The speed of light

The study of the speed of light is a fascinating and subtle issue that gives rise to a thousand questions.

1) "I can measure the speed of light?
No. The emergence of special relativity (and the fact that the constancy of the speed of light in any inertial reference system is a second postulate) has led to a change in the way they define the fundamental units. Today, the meter is defined com the way light travels in 1 / 299792458 s. The second is defined by an atomic transition frequency (which is a standard that is already obsolete given the new watches "source" with precision measurements of time which is at around 10 ^ {-16} s). Measuring the speed of light is therefore a tautology since the meter must first be defined using the propagation of photons. In short, the speed of light c = 299792458 m / s is a definition, has no error because there is an observation. Someday

choose to define the unit of energy (mass) using a definition of hbarra, Planck's constant. This completes a remarkable fact. Newton's equation, F = ma, you have three variables to its right, time, length and mass. Simply define and apply two relationships. That would be c hbarra. It is extremely elegant.

2) What underlies the concept of the speed of light?
Causality. Photons and any massless particle propagating c. This is the maximum transmission speed of any signal. For Thus, implementing "causality." Causality has to do with the cause precedes the effect, but more refined means the action of energy deposited in a remote place. It's an idea sometimes confusing. Causality is associated with a cause do work elsewhere.

3) Does it violate causality the collapse of the wave function in quantum mechanics?
No. A measure gives us an immediate, information on the entire system. This does not mean to send a message immediately, or take action in a way that violates causality. For example, return from a trip to China, I open my suitcase and I have a black sock decoupled. I know in China another black sock. My information has been accurately instantly, has collapsed. But there is no photon transport or signs, no remote actions.

4) "Mathematically, what is the speed of light?
The propagator of a photon has a singularity on the light cone, which is defined by c ^ 2 t ^ 2 - (\\ vec x) ^ 2 = 0. This relationship follows from the Poincaré invariance. All Poincare invariant theory with massless propagators have the same light cone and, therefore, traveling acy define causality. For a variation of c, Poincaré symmetry is violated.

5) Can violate the Poincare symmetry? Yes, there
conditions that violate this symmetry. A photon can travel in a curved space. Poincare symmetry is valid only locally (Einstein's equivalence principle). In geodesic space of curvature not zero, the photons define causality, but not travel to c. You may have other violations of Poincare symmetry with plates, Casimir effect or factual description of thermal baths or areas filled with electromagnetic fields.
(There is a world power behind the concept of time travel in space with worm holes and Hawking's idea to propose a principle of protection chronological order.)

6) Can you measure a variation of the speed of light?
is incredibly difficult. This would have, for example, the same experiment without license plates and the Casimir effect and see a difference. This can be done for the Casimir energy. The problem is that the effect is typically E / m ^ 4, where E is the vacuum energy difference m the electron mass. For example take the case thermal E \\ sim T ^ 4. The effect inside the Sun is suppressed by forty orders of magnitude.

7) I have read that has been transmitted signals v> c. Is it right?
Experiments bearing the seal of supralumínica speed are somewhat misleading. In these experiments, wave packets are sent as group velocity exceeds c. It is advertised as cumbersome. However, the wave packet of the higher frequency always travels at c. Are the precursors (Forerunners) to begin laying energy. Nothing in violation of the Poincaré symmetry, c is constant. Other speeds in a package, the com phase velocity, it is not associated with energy transport and is not subject to any restrictions.


A photon coming from a quasar at the edge of the universe must obey these laws so unflappable during 10 ^ 17 seconds.